Research Highlight: Tuned in to Whale Behavior

Audio recordings lead to possible acoustic identification of five rare beaked whale species

Jan 09, 2014

Scripps Institution of Oceanography, UC San Diego researcher Simone Baumann-Pickering and her colleagues are developing new techniques to study beaked whales, some of the most rare and elusive mammals on the planet. These small whales spend just a few minutes at the surface of the ocean before diving to depths of up to 3,000 meters (9,800 feet) for up to 135 minutes, a record for mammals.

Observing them directly is rare and until recently scientists had no idea about basic information on many species of beaked whales. This is where the Scripps Behavioral Acoustic Ecology Lab, led by Baumann-Pickering, comes in.

Instead of visual observations, the technique often used to study other whale species, Baumann-Pickering uses audio recordings to study beaked whales. Her research group deploys passive acoustic recorders on the seafloor for months at a time. Back in the lab, Baumann-Pickering uses spectral analysis to sort through the sounds, picking out characteristic signals made by each species of whale. Her goal is to understand beaked whale behavior and how human activities may be influencing it.

There are currently 21 species of beaked whales, more than any other cetacean group, and they have echolocation signals that are distinctly different from one another, unlike dolphin clicks that are highly similar. From echolocating bats it is known that the signals’ frequency content and duration is shaped by their respective niches and optimized for a certain prey. Baumann-Pickering and colleagues believe that niche separation and foraging strategies may have driven the evolution of species-specific beaked whale signals as well and would like to test this in the future.

Over the past six years of careful listening, Baumann-Pickering and colleagues have identified 10 types of species-specific echolocation signals. So far, they have positively tied five of these signals to known species, while the other five signals they hypothesize belong to species of beaked whales whose signals have not yet been reported. By comparing stranding and sighting information with acoustic findings, the team has identified which species might likely produce which signal. A species, such as Perrin’s beaked whale, that is only known from five stranded animals offshore southern California can now be observed acoustically at several sites over multiple years and scientists can learn about its habitat preference and foraging behavior.

Baumann-Pickering is lead author on a recent paper in the Journal of the Acoustical Society of America and a paper scheduled for publication later this month outlining these discoveries, funding for which has been chiefly provided by the Office of Naval Research (ONR). She said that these observations are just the first step in assembling a behavioral inventory that answers the questions of “Who is where when, and why?” A basic description of natural beaked whale behaviors is needed to find answers about their habitat use and prey.

“Beaked whales are some of the deepest-diving species in the world and appear to be particularly sensitive to sound exposure,” said Michael Weise, the Marine Mammal and Biology program manager at ONR. “ONR is interested in better understanding the effects of sound on these sensitive species, and Baumann-Pickering’s approach is an exciting area of research that holds immense promise in better understanding these elusive and little understood species.”

Ultimately, Baumann-Pickering hopes to learn if beaked whale populations are healthy and to what degree their behaviors are influenced by anthropogenic noise in the ocean. In recent years, there have been several mass strandings linked to ship sonar activity, but the reasons why these animals strand remains unclear. Their natural behavior must be understood before their response to unnatural phenomena can be identified, she said.

“There is strong evidence that at least some beaked whales – possibly all – react negatively to anthropogenic sounds,” said Baumann-Pickering. “There are circumstances that we don’t currently understand that causes those strandings.”

Studying such elusive animals is challenging but Baumann-Pickering said it comes with a nice side benefit: beaked whales are a reminder that there is still great mystery in the ocean that is waiting to be discovered.

– Jill Harris is a fifth-year graduate student in the laboratory of marine biologist Jennifer Smith